This photo shows a close-up of plastic bags containing plasma.
Media Advisory

NIH halts trial of COVID-19 convalescent plasma in emergency department patients with mild symptoms

Study shows the treatment is safe, but provides no significant benefit in this group


The National Institutes of Health has halted a clinical trial evaluating the safety and effectiveness of COVID-19 convalescent plasma in treating emergency department patients who developed mild to moderate symptoms of COVID-19, the disease caused by the coronavirus SARS-CoV-2.

An independent data and safety monitoring board (DSMB) met on Feb. 25, 2021 for the second planned interim analysis of the trial data and determined that while the convalescent plasma intervention caused no harm, it was unlikely to benefit this group of patients. After the meeting, the DSMB recommended that the National Heart, Lung, and Blood Institute (NHLBI), part of NIH, stop enrolling new patients into the study. NHLBI did so immediately.

Launched in August 2020, the Clinical Trial of COVID-19 Convalescent Plasma of Outpatients (C3PO) was being conducted at 47 hospital emergency departments across the United States and had enrolled 511 of the 900 participant recruitment goal. It was specifically looking at the effectiveness of COVID-19 convalescent plasma – blood plasma derived from patients who have recovered from COVID-19 – in adults who came to an emergency department with mild to moderate symptoms they had for a week or less. These patients also had at least one risk factor associated with severe COVID-19, such as obesity, hypertension, diabetes, heart disease, or chronic lung disease, but none were ill enough at the time to be hospitalized.

After the study participants received either the COVID-19 convalescent plasma or a placebo, researchers tracked whether the participants needed to seek further emergency or urgent care, had to be hospitalized, or died within 15 days of entering the trial. The recent data analysis from the study indicated no significant difference in the proportion of participants who experienced any one of these outcomes. Even if enrollment continued, this trial was highly unlikely to demonstrate that COVID-19 convalescent plasma prevents progression from mild to severe illness in at-risk emergency department non-hospitalized participants.  

COVID-19 convalescent plasma, also known as “survivor’s plasma,” contains antibodies, or special proteins, generated by the body’s immune system to the novel coronavirus. More than 100,000 people in the United States and many more worldwide have already been treated with it since the pandemic began.


Nahed El Kassar, M.D., Ph.D., program officer for the C3PO trial and a medical officer with NHLBI’s Epidemiology and Clinical Therapeutics branch, or Simone Glynn, M.D., M.P.H., program scientist for the C3PO trial and chief of the NHLBI’s Blood Epidemiology and Clinical Therapeutics branch, are available for interviews.


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